1. Field of the Invention
The present invention relates to a compact zoom lens suitable for use in video cameras and still video cameras, a camera apparatus using the zoom lens, and a portable information terminal apparatus.
2. Discussion of the Background
In a zoom lens for use in video cameras and still video cameras, recently, as demands for a higher zooming ratio, a wider field angle and a higher resolution increase, and at the same time for meeting demands for a smaller size, a lighter weight and a reduced cost, reducing the overall length and the outer diameter of the zoom lens and decreasing the number of pieces of lens composing the zoom lens are becoming imperative.
As a zoom lens for meeting the above-described demands, a type of zoom lens has been proposed, in which, in order from the object side, a first lens group having a positive refracting power, a second lens group having a negative refracting power, a third lens group having a positive refracting power, a fourth lens group having a positive refracting power, and a fifth lens group having a positive refracting power are arranged. By moving the second lens group toward the imaging plane side, zooming of the zoom lens from the short focal length end to the long focal length end is performed, and a shift in the position of an imaging plane of the zoom lens due to the movement of the second lens group for the zooming is corrected by the fourth lens group.
Japanese Patent Laid-open Publication No. 6-180424, Japanese Patent Publication No. 3109342, and Japanese Patent Laid-open Publication No. 9-90221 describe examples of zoom lenses of such type. In each of the zoom lenses of these examples, a shift in the position of an imaging plane occurring in connection with zooming is corrected by movement of the fourth lens group.
Each of the zoom lenses having five lens groups described in the above publications, respectively, is configured such that the fourth lens group is moved solely for correcting a shift in the position of an imaging plane occurring in connection with zooming, and the movement of the fourth lens group does not contribute to the zooming at all. The function of zooming is mostly performed by the second lens group. For this reason, the moving amount of the second lens group for zooming is large, and as a result, the first lens group must be arranged at a distant position from an aperture diaphragm arranged in the third lens group. This leads to increasing the size of the first lens group and furthermore to increasing the overall size of the zoom lens.